<template>
	<div class="list">
		<div class="item" 
			v-for="item of letters" 
			:key='item'
			:ref='item'
			@touchstart.prevent='handleTouchStart'
			@touchmove='handleTouchMove'
			@touchend='handleTouchEnd'
			@click="handleLetterClick"
			>{{item}}</div>
	</div>
</template>

<script>
	export default {
		name: 'CityAlphabet',
		props: {
			cities: Object
		},
		computed: {
			letters (){
				const letters = []
				for(let i in this.cities) {
					letters.push(i)
				}
				return letters
			}
		},
		data () {
			return {
				touchStatus: false,
				startY: 0,
				timer: null
			}
		},
		updated () {
			this.startY = this.$refs['A'][0].offsetTop
		},
		methods: {
			handleLetterClick (e) {
				this.$emit('change', e.target.innerText)
			},
			handleTouchStart () {
				this.touchStatus = true
			},
			handleTouchMove (e) {
				if (this.touchStatus) {
					if (this.timer) {
						clearTimeout(this.timer)
					}
					this.timer = setTimeout(() => {
						const touchY = e.touches[0].clientY - 79
						const index = Math.floor( (touchY-this.startY) / 20 )
						if ( index >= 0 && index < this.letters.length ) {
							this.$emit('change', this.letters[index])
						}
					})
					
				}
			},
			handleTouchEnd () {
				this.touchStatus = false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display: flex
		flex-direction: column
		justify-content: center
		position: absolute
		top: 1.58rem
		right: 0
		bottom: 0
		width: .4rem
		.item
			line-height: .4rem
			text-align: center
			color: $bgColor
</style>